Update isc-dhcp4 package to 4.2.4p1 (ISC DHCP 4.2.4-P1).
Fixes security problems.

Changes since 4.2.4

! Previously the server code was relaxed to allow packets with zero
  length client ids to be processed.  Under some situations use of
  zero length client ids can cause the server to go into an infinite
  loop.  As such ids are not valid according to RFC 2132 section 9.14
  the server no longer accepts them.  Client ids with a length of 1
  are also invalid but the server still accepts them in order to
  minimize disruption.  The restriction will likely be tightened in
  the future to disallow ids with a length of 1.
  Thanks to Markus Hietava of Codenomicon CROSS project for the
  finding this issue and CERT-FI for vulnerability coordination.
  [ISC-Bugs #29851]
  CVE: CVE-2012-3571

! When attempting to convert a DUID from a client id option
  into a hardware address handle unexpected client ids properly.
  Thanks to Markus Hietava of Codenomicon CROSS project for the
  finding this issue and CERT-FI for vulnerability coordination.
  [ISC-Bugs #29852]
  CVE: CVE-2012-3570

! A pair of memory leaks were found and fixed.  Thanks to
  Glen Eustace of Massey University, New Zealand for finding
  this issue.
  [ISC-Bugs #30024]
  CVE: CVE-2012-3954

(taca)